The invention relates to formulations comprising methyl propyl ketone peroxide and the use of methyl propyl ketone peroxide-containing formulations in the process to cure unsaturated polyester resins.
Ketone peroxides and their use as curing agents for unsaturated polyester resins also have long been known. A ketone peroxide is a reaction product of a ketone and hydrogen peroxide and usually is a mixture of products with different structure types. The so-called type-3 and type-4 structures (see below) are most stable and are therefore predominantly present. Most of the ketone peroxides in pure form are hazardous and they need to be phlegmatized to a degree where they are safe to handle and transport, typically at ambient temperature, as mentioned in, for instance, U.S. Pat. No. 3,649,546. The degree of phlegmatization or, in other words, the amount of a phlegmatizer needed, is dependent on the type of ketone peroxide, type of phlegmatizer and the relative weight of the various ketone peroxide types. It has been tried to influence the ratio of the compounds in equilibrium in such a manner that a relatively safe mixture of compounds is formed, one that needs little phlegmatization. U.S. Pat. No. 3,560,395, for example, discloses how to make aqueous methyl ethyl ketone peroxide compositions containing just hydrogen peroxide, a ketone peroxide of formula: 
(a so-called type-4 ketone peroxide), and water, which is safe at concentrations of more than 10% active oxygen and gives fast curing of water extended polyester resins. The production and the generic use of predominantly type-4 ethyl amyl ketone peroxide was disclosed in U.S. Pat. No. 3,151,170. This document does not disclose that other types of ketone peroxides solve many of the problems depicted above. U.S. Pat. No. 4,052,465 discloses the use of ketone peroxides consisting essentially of compounds of the formula: 
(so-called type-3 ketone peroxides) for the curing of vinyl or vinylidene group-containing polyester resins.
JP-A-10087652 discloses the use of a ketone peroxide composition comprising 13-43% by weight of the type-3 product and 3-22% by weight of the type-4 product. When used to cure unsaturated polyester resins, the compounds are said to give a long gel time and slow cure. Safety properties of peroxides are not discussed. However, such formulations were found not to be safe and the cure of the UP was found to be too slow. Typically, the ketone peroxides exemplified are derived from methyl ethyl ketone and use is made of conventional accelerators, such as Co-octoate.
However, the methyl ethyl ketone peroxides disclosed in the examples of these references show insufficient performance in the curing of gel coats, being thin layers (up to 2 mm in thickness) of unsaturated polyester resin. More specifically, an undesired and very long gel time is observed, resulting in, inter alia, too high styrene emission. Gelation and cure speed can be increased by using higher amounts of peroxide and/or by introduction of cobalt salts, such as cobalt octoate. However, in the conventional systems this leads to unacceptable discoloration of the gel coats. Also, conventional fast curing systems tend to lead to foaming in vinylester resins, which is undesired. Slow cure is a disadvantage in most of the other applications of unsaturated polyester resins too. Moreover, some of the ketone peroxide formulations of the prior art that contain a large amount of type-3 ketone peroxide are not safe. Furthermore, the use of aqueous compositions, as proposed by the prior art, is unacceptable in many applications since i) conventional Co-based accelerators hydrolyze in such systems, leading to unsatisfactory cure characteristics, and ii) aqueous formulations tend to result in undesired foam formation. Hence, there is a clear need for improved ketone peroxide compositions which should give fast cure, do not lead to the hydrolysis of Co-based accelerators, give low discoloration, give no foaming of vinylester resins, and at the same time are safe during transport, storage, and handling, preferably at ambient temperatures.
Surprisingly, we have found that specific ketone peroxide formulations that are derived from methyl propyl ketone and comprise a high amount of type-4 ketone peroxide can be produced safely, especially when use is made of an effective amount of particular (co)solvents, and that the use of these products gives desirable fast curing rates of unsaturated polyester resins, especially in gel coat applications, and that a low level of residual monomer is obtained. Moreover, the products according to the invention can be stored and handled safely at ambient temperatures and solve most, if not all of the other problems.
Accordingly, we claim methyl propyl ketone peroxide formulations comprising: more than 60%, preferably more than 65, more preferably more than 67%, most preferably more than 70% by weight of type-4 methyl propyl ketone peroxide up to 100%, preferably 99, more preferably 98%, most preferably 95% by weight of type-4 methyl propyl ketone peroxide, and preferably comprising, less than 40%, preferably less than 35%, most preferably less than 30%, and preferably more than 1%, more preferably more than 2%, most preferably more than 5% by weight of type-3 methyl propyl ketone peroxide (calculated as the amount of active oxygen of the specified type ketone peroxide based on the total active oxygen of all methyl propyl ketone peroxides in the formulation) and a non-aqueous phlegmatizer in an amount such that the Self Accelerating Decomposition Test (SADT), Dutch Pressure Vessel Test (DPVT) and the Koenen test show safe handling and transport at temperatures of 0-50xc2x0 C., preferably at temperatures of 10-45xc2x0 C., most preferably at ambient temperatures of 20-40xc2x0 C. More preferably, the amount of phlegmatizer is chosen such that the self accelerating decomposition temperature as determined by the SADT is 50xc2x0 C. or higher, the limiting diameter as determined by the DPVT is  less than 3.5 mm, and the limiting diameter as determined by the Koenen test is 1.0 mm. The tests are of the conventional type as mentioned in the UN Recommendations on the Transport of Dangerous Goods, 11th edition (ST/SG/AC.10/1/Rev.11)
Preferably, the final methyl propyl ketone peroxide formulation contains more than 10%, preferably more than 15%, more preferably more than 20, and most preferably more than 25% by weight of type-4 peroxide, based on the weight of the total formulation. Preferably, the amount of type-3 ketone peroxide in the formulations according to the invention is less than 13% by weight, based on the weight of the total formulation. It is noted that the amount of active oxygen associated with each of the peroxidic components is determined in the conventional way known in the art and that hydrogen peroxide is not a ketone peroxide. Furthermore it is noted that the term methyl propyl ketone peroxide includes peroxides derived from methyl isopropyl ketone and/or methyl n-propyl ketone. Preferred are the methyl isopropyl ketone-derived peroxide formulations.
The final methyl propyl ketone peroxide formulations may contain (residual) hydrogen peroxide. It was observed that in certain curing processes of unsaturated peroxides the speed of gelation was increased due to the presence of the H2O2. However, in some instances, such as when vinylester resins are cured, the presence of H2O2 is undesirable as it gives foaming. Therefore, depending on the use of the formulations, it can be preferred to have from 0.001 to 5% by weight (% w/w) of hydrogen peroxide (based on the weight of the active oxygen of the hydrogen peroxide over the weight of the total active oxygen of the formulation) in the formulation.
Phlegmatizers that can be used in these formulations are of the conventional type and are preferably selected from alkanols, cycloalkanols, alkylene glycols, alkylene glycol monoalkyl ethers, cyclic ether substituted alcohols, cyclic amides, esters, ketones (preferably other than the ketone that is used to make the ketone peroxide being phlegmatized), aromatic solvents, halogenated hydrocarbon solvents, and mixtures thereof.
Examples of hydrophilic esters include, but are not limited to, monocarboxylic esters of mono- and dihydric alcohols, esters of dicarboxylic acids and monohydric alcohols, carbonates of monohydric alcohols, alkoxyalkyl esters, xcex2-keto esters, phthalates, phosphates, benzoates, adipates, and citrates. More specific examples of esters useful in most of the compositions of the present invention are dimethyl phthalate, diethyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, diallyl phthalate, isopentyl acetate, benzyl acetate, methyl benzoate, ethyl benzoate, isopropyl benzoate, diethylene glycol dibenzoate, dipropylene glycol dibenzoate, propylene glycol dibenzoate, n-butyl pivalate, isoamyl pivalate, sec-amyl pivalate, diethyl adipate, dioctyl adipate, methyl neodecanoate, n-butyl neodecanoate, propylene glycol diacetate, ethylene glycol diacetate, neopentyl acetate, methyl-2-ethythexanoate, isoamyl propionate, sec-amyl propionate, benzyl propionate, butyl caproate, ethylene glycol dipropionate, heptyl propionate, methyl phenyl acetate, propyl caprylate, triethyl phosphate, tricresyl phosphate, trixylyl phosphate, dimethyl methyl phosphonate, chlorinated phosphate esters, tributyl phosphate, tributoxyethyl phosphate, methyl decanoate, dimethyl succinate, diethyl succinate, dimethyl malonate, diethyl malonate, methyl ethyl succinate, diisobutyl nylonate, 2,2,4-trimethyl-1,3-pentanediol-diisobutyrate (also known as TXIB), diethyl oxalate, dimethyl fumarate, diethyl fumarate, dipropyl fumarate, dibutyl fumarate, acetyl tributyl citrate, and diesters of maleic anhydride, such as dibutyl maleate.
Preferred useful hydrocarbon solvents include, but are not limited to, benzene, toluene, ethylbenzene, xylene (o, m, p, or mixtures thereof), mesithylene, o-diisopropyl benzene, m-diisopropyl benzene, p-diisopropyl benzene, and mixtures thereof. More preferred hydrocarbon solvents include Solvesso(copyright) 100, Solvesso 150, Solvesso 200, halogenated versions of these compounds, such as p-dibromobenzene, 5-bromo-m-xylene, and 1,2,3-trichlorobenzene, and mixtures of two or more of any of the compounds. Most preferred are aromatic solvents, since these show the best solubility for MPKP formulations with a high type-4 content.
Useful halogenated hydrocarbons include 3-bromo-o-xylene, 4-bromo-o-xylene, 2-bromo-m-xylene, 4-bromo-m-xylene, 5-bromo-m-xylene, o-dibromobenzene, p-dibromobenzene, tetrabromoethylene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, and mixtures thereof.
Examples of ketone as solvents are 4,4-dimethyl 4-hydroxy-2-pentanone, disobutylketone and diisopropyl ketones.
Examples of cyclic amides include 2-pyrrolidone, N-methyl pyrrolidone, 1,5-dimethyl-2-pyrrolidone, and 3,3-dimethyl-2-pyrrolidone.
Examples of useful alcohols are n-butyl alcohol, capryl alcohol, tetrahydrofurfuryl alcohol, 1,4-dihydroxymethyl cyclohexane, ethylene glycol, diethylene glycol, polyethylene glycols, propylene glycol, dipropylene glycol, neopentyl glycol, hexylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, butene diol, 1,5-pentane diol, 2,2,4,4-tetramethyl-1,3-cyclobutane diol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetrahydrofuran and diacetone alcohol.
Soluble solid or waxy materials that can be employed in the compositions of the present invention include polyethylene glycol, polypropylene glycol, polytetrahydrofuran, and polycaprolactone.
Preferred methyl propyl ketone peroxide (MPKP) formulations according to the invention comprise a phlegmatizer selected from the group consisting of dimethyl phthalate, and 2,2,4-trimethyl-1,3-pentanediol-diisobutyrate. However, other phlegmatizers selected from one or more of the compounds given above may be used as a co-phlegmatizer in the preferred methyl propyl ketone peroxide formulations. When a co-phlegmatizer is used, preferably at least 1% by weight, more preferably at least 10% by weight of all phlegmatizer is of the preferred type. The use of one or more of these two phlegmatizers allows the production of safe MPKP formulations with high active oxygen levels which are stable during storage (no change in the ratio type-3:type-4 product is observed) and which give very good curing of unsaturated polyester resins.
It is noted that U.S. Pat. No. 5,907,022 discloses, in a comparative example, how to make a pure type-3 ketone peroxide based on methyl isopropyl ketone. However, neither safe, stable, and technical mixtures comprising type-3 and type-4 ketone peroxide nor the use of such products in unsaturated curing processes is disclosed or suggested.
The curing process of the present invention comprises the addition of an MPKP formulation according to the invention to one or more conventional resins and/or pre-polymers, and preferably at least one accelerator, followed by mixing and dispensing. The curing process is preferably carried out at ambient temperatures commonly used in applications such as hand lay-up, spray, and coating. However, it can also be used in SMC, BMC, pulltrusion techniques, and the like. Due to the high reactivity of the MPKP formulations according to the invention they are particularly suitable for curing (at ambient temperature) of a thin articles of up to 2 mm in thickness and coating, especially gel coats. The amount of the MPKP formulation that is to be used in the curing process ranges from 0.1 to 8% by weight based on resin, but preferably from 0.5 to 5%, most preferably from 1 to 2%.
The resin or pre-polymer is preferably chosen from the group consisting of conventional unsaturated polyesters, including so-called ortho resins, iso-resins, iso-npg resins, and dichloro pentadiene resins. Examples of such resins are maleic, allylic, vinylic, and epoxy-type materials, combined with at least one ethylenically unsaturated reactive monomer. Preferred ethylenically unsaturated reactive monomers include styrene and styrene derivatives such as xcex1-methylstyrene, indene, divinyl benzene, stilbene, dibenzalacetone, propenyl benzene, and isopropenyl benzene; triallyl cyanurate, triallyl isocyanurate, and mixtures thereof. The amount of ethylenically unsaturated reactive monomer is from 0 to 50% by weight (% w/w), based on the weight of the resin.
Preferred optional accelerators are selected from the group consisting of conventional salts, preferably cobalt salts, of one or more carboxylic acids with one or more of the metals and complexes of two metals selected from lithium, copper, manganese, magnesium, vanadium, iron, and cobalt, with an oxygenated compound, such as an aldehyde, ketone, ether, ester, or alcohol. More particularly, the oxygenated compound of the complexes is preferably selected from keto- and aldo-esters and ethers or alcohols, in particular methyl acetoacetate, ethyl acetoacetate, mono- and diesters of ketoglutaric acid, pyruvates, sugars such as glucose and fructose; and esters of ascorbic acid such as ascorbic palmitate; 1,3-diketones and aldehydes, in particular acetyl acetone, benzoyl acetone, and dibenzoyl methane; mono- and diesters, more in particular diethyl malonate and succinates; 1,2-diketones, in particular diacetyl and glyoxal; and certain polyalcohols and other alcohols such as diethylene glycol, benzyl alcohol, and alcohols of the fatty series, as disclosed in U.S. Pat. No. 5,235,010. In the process of the present invention, the accelerator is generally employed in a conventional amount. Amounts of 0.1 to 5% by weight, preferably 0.25 to 2.0% by weight, based on the weight of the resin, are typically used.
Other optional additives may be employed in the curing process according to the invention, such as fillers, glass fibres, pigments, inhibitors, promoters, and stabilizers.
In the curing process of the present invention, typically the resin is first mixed with the ethylenically unsaturated reactive monomer. The optional accelerator composition may be added in several different manners and may have been pre-mixed with the monomer or resin. The MPKP formulation may be added directly to the mixture. However, it can also be first mixed with the monomer or resin. Care is to be taken that the MPKP formulation and the accelerator are not pre-mixed, since this can be hazardous.
The curing process of the present invention is preferably carried out at ambient temperature, but depending on the technique being used, temperatures up to 150xc2x0 C., more preferably up to 50xc2x0 C., can be used.
The invention is elucidated by means of the following examples: